The heterogeneous network becomes a research hotspot of mobile communications because it can realize the optimization of system performance by improving the topological structure of the network. The heterogeneous network is composed of a high-power macro base stations and low-power nodes of network planning. The low-power nodes are under the coverage of the macro base stations and placed autonomously. The low-power nodes include a femtocell, a pico-cell, a relay station, and so on, which can realize coverage of hotspot region and shunt of cell services, so that a cell splitting gain is obtained. Because the power and coverage of different types of base stations are different, and the low-power node placed autonomously, the interference problems of control channels and service channels of different base stations are very outstanding in the heterogeneous network, so the heterogeneous network faces huge technical challenges.
In the next generation evolution system, for example, the 3GPP-LTE-A standard, enhanced Inter-Cell Interference Coordination (eICIC) schemes are adopted to solve the interference problems. The eICIC is one of the symbol key technologies in the LTE-A for improving the cell edge coverage and realizing the Range Extension (RE) with the intent to shunt the cell services. The eICIC schemes are divided into two types: an eICIC scheme based on the CA technology and the other eICIC scheme based on the time-domain Almost Blank Subframe (ABS). The ABS realizes service silence by configuring ABS subframes in an interfered cell, and the interfered cell uses these ABS subframes to provide services for users strongly interfered in the cell, so that the coordination of interferences between the cells is realized.
As one of the key technologies, the CA can not only provide a high-speed service on a large bandwidth formed by aggregation, but also can avoid interferences in a frequency domain which realizes the heterogeneous network at a Component Carrier (CC) resolution level. It is supposed that the bandwidth of the heterogeneous network is composed of two CCs, namely f1 and f2. In order to realize the interference coordination between the macro base station and the pico-cell, the f1 and f2 can be allocated to the users of the macro base station and the pico-cell respectively, so as to avoid the interferences of the service channel and the control channel of the users. Or, a cell centre user of the pico-cell can be allocated with the same CC as the macro base station, and an edge user is allocated with the CC different from that of the macro base station. The disadvantage of the scheme is that it can only be adopted by the LTE-A users, but cannot be compatible with the LTE users. The application of all the above technologies has an important premise, that is, the problem of selecting a user service cell from the cells needs to be solved at first. In a cellular mobile communication network, all users have a home service cell, which provides the users with broadcasting, service transmission and other services. In a traditional homogeneous network, selecting the user service cell is based on the measurement of received signal intensity. In the heterogeneous network, because the transmission power of added nodes is far lower than that of the macro base station, a method for selecting a service cell based on the received signal intensity will cause a very small coverage range of these nodes and does not realize the maximization of cell splitting gain. For the purpose of boosting the priority of the low-power nodes and extending the coverage range of the low-power nodes, the 3GPP meeting launches researches and discussions, and provides some cell selection and reselection algorithms in the enhanced LTE-A heterogeneous network, which mainly include an RE algorithm and a path loss algorithm presented by Qualcomm. The core idea of the RE algorithm is that in the traditional service cell selection algorithm, a bias value which is greater than 0 is added to the Reference Signal Receiving Power (RSRP) of the low-power node, and the bias value of the RSRP of the macro base station is 0, so as to reduce the threshold of the low-power node and increase the chance of a UE to select the low-power node as the serving cell. In the cell selection algorithm based on path loss, each UE selects the cell with the minimum path loss as the serving cell.
The above method obviously enlarges the coverage range of the low-power nodes, which is even similar to the macro base station. But for the users at the coverage edge of the low-power nodes, even though an interference elimination means is adopted to eliminate the influence of a strong interference source, a downlink Signal to Interference plus Noise Ratio (SINR) is very low due to the too low transmission power of its serving cell (the low-power node), therefore the spectral efficiency of the cell is reduced.
When a multi-antenna technology is adopted, the inter-cell interference coordination can be further performed in the spatial domain; for example, in a Coordinated Multi-Point (CoMP) transmission technology. Through the interaction of channel information of the mobile users between adjacent cells, the adjacent cells adopt a certain interference avoiding policy to the edge users or multiple cells perform joint transmission to the mobile users, thereby improving the throughput of the edge users and increasing the coverage of high data transmission rate, reducing the interferences of the edge users, and improving the throughput of the cells. In the heterogeneous network, the CoMP transmission technology can serve as an enhancement of the eICIC technology, and can further increase the system capacity based on a gain obtained by the eICIC technology.
At present, the cell selection and interference management are two independent processes. The cell selection increases the number of users of the low-power node through load balancing, and the interference management is used for solving the problem of the increase of inter-cell interferences. With the increase of density of the low-power nodes, if the processing is continued according to the above method, the complexity of an interference management algorithm will increase sharply, and the effectiveness of the interference management algorithm will be reduced, thus influencing the increase of the number of low-power node users.